text:
How does wind affect the airspeed that I should fly for maximum range in an airplane?
I have heard that wind affects the actual airspeed that I should fly for maximum range in an aircraft.
I understand that wind will not affect the airspeed that I should fly if I am looking for maximum endurance, but what about maximum range?
How (and how much) should airspeed be adjusted for wind in order to get maximum range?

uniform wind (always constant head or tailwind) wouldn't affect best airspeed I believe.

@ratchetfreak From my understanding, it does.  You should fly faster into a headwind in order to minimize the time that it affects you,  and vice versa for tailwinds.

@Lnafziger - That's why he said uniform winds not variable winds :).  But I would imagine there is some strategy to finding tail winds and avoiding headwinds.  Much like navigating a river...you know,finding a strong current going the same way you are.

@JayCarr I am referring to uniform winds as well.  A uniform headwind or a uniform tailwind. :)

@Lnafziger - I appear to be mixing my lingo up again, apologies.  My only point is that ratchet freak was referencing having constant tail winds or constant headwinds for the duration of the flight.  But I think your question is asking about situations where there are both (which seems more likely in real life anyway...maybe?)

@JayCarr No, my question is regarding a particular wind condition, not one that is changing.

My answer was rather concise first, and I got the impression that I need to elaborate the question first. The question is about the best airspeed for maximum range. With wind. Best range means you cover the most distance while the wind is carrying the plane with it. If you have a headwind, the longer you stay aloft, the more you are carried back, so you better hurry up. With a tailwind, it helps to slow down because now the wind is helping you to cover even more distance.
But how much? We need to pick that particular speed where the change in fuel consumption just balances the change in speed over ground. I always found that easier to explain with gliders, and there you can really observe which polar point is best. Just picture yourself as an observer on the ground who sees the plane fly by in the distance. If you plot a line with the combination of positions and altitude, there must be one flight speed that produces a line where the flight path angle is the shallowest. This is the desired optimum. That has only little to do with optimum L/D - this is just one other point you can find with a sink speed polar. And it happens to be the point for best glide in still air. But there is so much more that humble polar will tell you, if you look at it the right way.
With powered aircraft you need to pick the polar point where your fuel flow is lowest for the given speed over ground. Basically, you fly like the glider and add enough power to stay at the same altitude. That is all the difference. User2168 has answered that part already with a graphical solution.
OK, now back to gliders. Please look at the plot below which shows airspeed on the X axis and sink speed on the Y axis.

The solution is graphical: You start on the X-axis at the point which corresponds to the wind speed and put a tangent on the sink speed graph. Where the tangent touches the sink polar (blue line), the plane flies at the best L/D for that given wind speed. Move the starting point to positive speeds for headwind and to negative speeds (not shown here) for tailwind. If the term "best L/D" is already reserved in your mind, please read this as the "best polar point". It is really the same.
Since User2168 has beaten me to the graphical solution, I will add an analytical solution.
For powered flight things become more tricky, because thrust changes with speed. To simplify things, we can say that thrust changes over speed in proportion to the expression $v^{n_v}$ where $n_v$ is a constant which depends on engine type. Piston aircraft have constant power output, and thrust is inverse with speed over the speed range of acceptable propeller efficiencies, hence $n_v$ becomes -1 for piston aircraft. Turboprops make some use of ram pressure, so they profit a little from flying faster, but not much. Their $n_v$ is -0.8 to -0.6. Turbofans are better in utilizing ram pressure, and their $n_v$ is -0.5 to -0.2. The higher the bypass ratio, the more negative their $n_v$ becomes. Jets (think J-79 or even the old Jumo-004) have constant thrust over speed, at least in subsonic flow. Their $n_v$ is approximately 0. Positive values of $n_v$ can be found with ramjets - they develop more thrust the faster they move through the air.
Now for fuel flow: This goes up and down with the power output of the engine. Again a simplification, but it helps to get to grips with the problem and gives useful results. This lets us re-formulate the problem as: At what airspeed do I have the best ratio between power and ground speed?
Mathematically, we want to fly with $\frac{P}{v_w+v}$ at the lowest possible value. $P$ is the power, $v_w$ is the wind speed and $v$ the airspeed. To express the thrust behavior over speed, I break P up into a product of a constant $K_S$, the throttle setting $\delta$ and the speed like this: $K_S\cdot\delta\cdot v\cdot v^{n_v}$. Here is the general solution, pasted as a PNG to save me all the typing in the editor:

Please note that implicitly the lift coefficient is on both sides of the equation. To solve it, you need to do it recursively, until speed and lift coefficient match. I took this form because of the similarity to the general form at still wind which can be found in many performance books. This here I didn't find anywhere, and it took me a while to figure it out. Thank you, Lnafziger, for the excellent question! It gave me a chance to learn something.
Now I have put the results into a plot. In order to eliminate the aircraft-specific parameters, it shows the ratio of $c_L$ with wind over $c_L$ without wind. The plot is metric, but will work for all units if you use the same units for wind speed and air speed.

To give an example for the application of the correction factor: If you are flying in a 20 m/s headwind and your best range speed at still wind is 50 m/s (approx 97 kts), the $c_L$ needs to be 70% of the $c_L$ at still wind for piston-powered aircraft. This makes your corrected airspeed 60 m/s (v is proportional to $\sqrt{c_L}$), and now the recursive nature of the formula rears its ugly head. At 60 m/s, the correction is only 77.5%, so we need to do a few loops until we arrive at a point where the airspeed and the correction factor match. In this example, this would be 57 m/s or 110 kts in case of a piston-powered aircraft.

@user2168: What is best depends on the circumstances. The question makes it clear that the polar point for best range with wind is requested. And that does change with wind.

I still believe that you mean to say glide ratio instead of best L/D here.  Glide ratio is in reference to the ground, while L/D is simply lift -vs- drag and has nothing to do with ground track.

If you reserve the expression "best L/D" for the still wind condition, please let me know how to say best ratio of lift to drag for optimizing range in a headwind. We need to be able to express somehow that a particular L/D ratio is meant.

@user2168: Best L/D is $V_x$ for zero power ($V_x$ depends on power setting). See How It Flies 7.5.4 (last paragraph of the section).

This is a great answer that describes the issue very well in engineering terms.  Is there a short, practical application of it that pilots can use to make speed corrections with?

The formula contains aircraft-specific values, so there is no way to make generalized, specific conclusions. I would suggest to compile a table of optimum speeds for different wind speeds, wing loadings and altitudes for a specific aircraft. And please keep in mind that this formula uses the parabolic polar approximation. If you know your airplane's polar in more detail, the quality of the table can be improved further.

I don't know if giving thanks is considered correct here, but the contributions of Peter Kämpf are so extensive, interesting and clearly worded that thanking him for his efforts is the least thing I can do...

This simply boils down to energy required to move from point A to point B, conveniently measured in fuel consumption, or, with gliders, distance gained per altitude given.  Under no wind conditions, under power we fly at the air speed where wing and engine/prop are most efficient, near Vy, and with gliding, Vbg.
Going into the wind is where you pay the devil his dues.  This becomes critical when you have an emergency power out into a 20 knot headwind and your landing field is ahead of you.  Might be easier to turn and fly to a field you already passed (altitude permitting).
Another alternative is  increasing speed above Vbg to get more distance into the wind.
It's no longer about the airspeed, it's about respect to ground.  You must reach that point anyway you can to land safely.
A chart or graph of max glide distance W.R.T. ground into headwinds would be extremely useful information for any aircraft (listed as best airspeed under those conditions).

Airspeed is your speed through an air mass, wind speed or direction will not change your airspeed. What wind direction changes is your ground speed, which is the speed of the aircraft over the surface of the earth. A headwind component reduces your ground speed, while a tailwind increases it. What I think you are asking is how you change your airspeed to best use fuel depending on whether you have a headwind or tailwind.
The general answer to this is that if you have a headwind you would increase your airspeed, and with a tailwind reduce it. If you have a headwind you will take longer to get where you are going, so increasing airspeed will get you there faster and you will use less fuel. A tailwind gets you there faster so you can reduce your airspeed and therefore fuel burn and still get there in the same amount of time as you would if you were in still air.
In practice whether you do this depends on how much of a headwind/tailwind component you have, and what your burn rates are at different airspeeds. Aircraft have a speed/drag curve, at some point the energy you add to go faster just ends up being wasted. You can also get behind the drag curve, flying too slow to be efficient. Adding a bit more speed may make sense, adding a load more speed will likely end up in using more fuel without much result. The opposite is also true, you can end up getting too slow and draggy, burning more fuel.

So how do we determine how much to correct?   Can you provide an example?

In my case I fly light aircraft, Cessna 172s and PA-28s. If I had a substantial headwind I would increase from 2300 rpm to 2450 or so rpm to add another 5-10 knots of cruise - any more isn't good for the engine. If I had a big tailwind I might reduce to 2100 rpm and lose 5-10 knots of cruise. It's not much for me really, airliners have much more speed to play with, they have software to figure that out.

With a tailwind I believe you would get max range by flying at max endurance airspeed.  It gets a bit more complicated with a head wind as the answers above indicate.


text:
Why is an LPV WAAS GPS approach considered non-precision?
My understanding of precision was both lateral and vertical guidance. If a GPS approach with WAAS provides both, why is it still considered non-precision?

I believe I've seen the explanation somewhere around the site already, but it is not present in the similar question the search manages to find, http://aviation.stackexchange.com/questions/6341/is-lpv-considered-a-precision-approach (it only says it is non-precision, but not why).

@JanHudec This one?

@Pondlife, yes, that one looks like a good duplicate.

@JanHudec I think it's a dupe, but unfortunately the only answer on the other question doesn't make any sense (to me), unless I missed something. That doesn't change the dupe thing, of course.

@Pondlife the answer that is linked states that a non-precision approach with vertical guidance is considered that because onboard instruments compute the planes location. However with WAAS, there are ground based stations outside of the aircraft which help compute this.

@jskypilot Even with WAAS, the onboard GPS unit determines the aircraft's position, not the ground stations. And Wikipedia's list of SBAS solutions shows that they all (?) use ground stations.

@Pondlife Not sure if duplicate. The other question asks about why LPV SBAS is not a precision approach by ICAO. This one asks why LPV using the US SBAS is not a precision approach.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Why does the TAF provide forecasts at irregular intervals?
A TAF is published 4 times a day at 6 hour intervals. However if you look at the forecasts within a TAF one might be at a 4 hour interval and the next at an 8. Just look at this example:
TAF KPDK 071124Z 0712/0812 32009KT P6SM SKC
FM071600 33011G18KT P6SM FEW045
FM080000 32008KT P6SM SKC

Why not publish at consistent intervals?

I assume you're referring to the FM (FROM) groups. The TAF itself is published at regular intervals but sometimes the conditions are expected to change significantly in between those times; obviously, the weather doesn't operate on a neat schedule. So the TAF will show the expected time of those changes.
According to the National Weather Service:

FROM Group: ie. (FM1600)
The FM group is used when a rapid change, usually occuring in less
  than one hour, in prevailing conditions is expected. Typically, a
  rapid change of prevailing conditions to more or less a completely new
  set of prevailing conditions is associated with a synoptic feature
  passing through the terminal area (cold or warm frontal passage).
  Appended to the FM indicator is the four-digit hour and minute the
  change is expected to begin and continues until the next change group
  or until the end of the current forecast.
A FM group will mark the beginning of a new line in a TAF report. Each
  FM group contains all the required elements -- wind, visibility,
  weather, and sky condition. Weather will be omitted in FM groups when
  it is not significant to aviation. FM groups will not include the
  contraction NSW.

What does the contraction "NSW" mean and why wouldn't it be included? I've watched enough Australian V8 Supercars racing that the only thing coming to mind is "New South Wales", but I'm pretty sure that ain't it.

@FreeMan No Significant Weather. It makes no sense in a FROM group because if there was no significant weather, there wouldn't need to be a FROM group in the first place.

This is actually very simple.
The reason is because the conditions shown on a given line are implied to be current until the next line provides a change.  If the conditions forecast in a given line are expected for 3 hours, then the next line will be three hours later.  If it is 5 hours, then the next line will be five hours later.
When you see TEMPO, then those conditions replace the previous FM line, but only for the block of time in the TEMPO, and then it reverts back to the previous FM line's information until a new FM line replaces it for good.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why Do They Continue To Abbreviate Weather Products? Can We As A Community Change This?
Why are area forecasts, METARs, and TAFs written in an abbreviated manner? I understand that in the beginning, each digit or symbol costs money. However, that is no longer the situation. Why not make an area forecast as clear as possible? Aviators kill themselves because they do not understand the weather. Is there a reason the FAA continues to do this? Can the community of aviators change this?

"Aviators kill themselves because they do not understand the weather." I don't believe that is true, they kill themselves because they underestimate the weather and overestimate the equipment or skills. I don't believe any aviator died because they didn't understand a METAR or TAF and headed out anyway, they died because they either didn't read it at all or couldn't handle the conditions. Either way, reading a METAR or TAF is second nature to most airmen now, usually you get that in training.

For the same reason computer code is written in a language that isn't English, French, Spanish or other "natural" spoken language. It's confusing to the laymen but it's very well understood by those who have learned it.

The language of aviation is terse, compressed and intended to leave minimum room for interpretation or misapprehension.
It makes heavy use of formulas, themselves intended to to be unambiguous, but which are not always obviously and immediately meaningful to those who are unfamiliar with the language.
This is the norm for potentially critical communication in all fields that I'm aware of - the military, medicine and throughout the transportation industry.
The users of this language are trained in it; being familiar with it is an essential part of their competence.
Language, interfaces, procedures and tools in aviation don't need to be user-friendly, they need to be utterly precise, be usable in difficult circumstances, and on every occasion they're used have exactly the same outcome.
It's possible that an aviator has failed to understand a weather forecast and died as a result, but a weather reports that allowed themselves the liberty of free expression would kill a lot more than that.

It should also be noted that many weather observing stations like ASOS/AWOS are automated and report via low speed communication networks like dial-up, satellite, etc. The systems that report these are not complicated, often running small-scale microprocessors without a lot of memory.

Precisely, Ron Beyer. In addition, even when you've got (effectively) unlimited computing power, actually writing the code to extract the data is easier when you're looking for "OVC" instead of "Overcast", or "12012MPS" instead of "twelve metres per second from one hundred and twenty degrees".


text:
Why do the winglets go down on some cessnas?
I understand that the purpose of winglets is to decrease the wingtip vortexes to increase performance in climbs and cruising by redirecting the air over the wing. However on some old cessnas the winglets curve downwards. What is the reason for this?

A picture would be really helpful here, if you can find one.

@Pondlife The Cardinal II has wingtips that curve downwards, its difficult to get a good picture of it though.

http://s179.photobucket.com/user/Cardinal774/media/blog05cfo/wingtips.jpg.html is a good image to see a Cardinal II wingtip next to an older 177.

http://aviation.stackexchange.com/questions/22232/is-this-a-wing-tip-device-on-the-a-10-warthog has all the stuff you want in it.


text:
How do you set up your nav instruments and coms during ground operations and takeoff?
I have an HSI, an OBS, and a GPS. I normally set my HSI to runway heading, my bug to the wind direction, and the GPS to destination airport/waypoint (which will give me my turn out heading). I don't normally move my OBS. Once I get in line to depart, I set my bug to my departure heading.
For my coms I put the tower frequency in COM1 and the ground and guard in COM2.
Is there a standard procedure for setting up your nav instruments and coms? Is there a better or more efficient method than what I am doing? I have been thinking I could set my OBS up for the approach and my second option in COM1 as CTAF or tower at the arrival airport. What does everyone think?

"set my HSI", you mean the "course select pointer" (arrow)?  the only thing I would say is that if you have one COM antenna on the roof and another on the belly, use the radio attached to the roof antenna on Tower

I'm tempted to say this is too opinion-based and might be a better subject to discuss in chat - everyone has their own routines for this, and it's hard to say that one is more "correct" than another...

@voretaq7 I agree. Even leaving aside personal preferences, a lot depends on your equipment, VFR vs. IFR, airspace, ATC etc.

Even if there is not a single correct answer I would still like to read some of the best practices from experienced pilots.

Land-lubber question: What is an OBS? Is it the same as a CDI?

@TomMcW The OBS (omni bearing selector) is a knob on the CDI (course deviation indicator).  You select a course on the OBS and the CDI indicates whether you are left or right of it.   Depending on the aircraft and the specific CDI, it can get it's source for the actual course (to be compared with what you set on the OBS) from GPS, ILS, ADF or VOR.

I think it is save to say that it is a good practice to do anything you can on the ground rather then doing it in the air.
My setup: I usually end up with a similar set up as you do, though I don't use GPS much, but prefer hopping from one VOR to the next ;) (Well, I'll have to add that I'm not the most experienced pilot around here, for sure!)
Basic principle: I try to follow the rule I mentioned up there: I try to decrease the workload in the air by doing it on the ground already. That's why we make our route up on the ground, not as we go (well, one of the many reasons).
Let's say I have Com1 and Com2, each with a standby frequency as well as two Nav's, also each with a standby frequency: Before taxi, I'd have Com1 Active set up as tower and be listening and talking to Com2 to clearance, having ground in the standby. As soon as I have my clearance, I can put in my initial heading with the heading bug (not flying SIDs), as well as the Dep. frequency in Com1 Standby. This way I have all ground related stuff in Com2, all air related stuff in Com1. As for the Navs and the OBS: If there is a VOR at the airport I'm gonna put it in Nav2 and turn the OBS to initial takeoff heading (mostly runway heading). This is just as a support, "heading" still means pointing your nose to where the controller says, no matter what track the wind makes you actually fly. But then I know where I'm at and can already figure out what the wind is doing on my climb out. Nav1 goes to my first VOR, and depending whether I go direct or join an airway, I center the needle or set the OBS to the airway track respectively. The standby frequencies of the Navs are set to my second waypoint on Nav1, and whatever I think I'll need afterwards on Nav2. After takeoff I use Nav1 primarily to navigate, and Nav2 to verify my position (such a aircraft would usually have DME, so that you don't need to cross bear your position with two VORs, but if there is time to do so, why not).
In the air I usually don't use  the standby freqs much on the Coms, and just swap Com1 and Com2 when changing frequency. Before landing, the same thing counts as before takeoff: Take as much workload off in advance. Thus I'm setting up the coms (I got 3 spare frequencies when talking to approach or center or whatever, the'll all be filled in with usefull frequencies like ATIS, Tower and Ground), the Nav's for the approach (with missed approach in standby if available).
Well that was quite a novel, I hope you didn't fall asleep halfway through. This is what I do, and I get along with it quite well. I am not saying it is the 100% perfect thing to do, and (as Simon points out in his answer) you should do whatever you feel the most comfortable with.
Summing up, I think doing as much as you can in advance is key in flying (especially IFR), as it gives you more time in case you need it for something else to do.

I do think that the question is largely opinion based but paradoxically, that's why I'm offering an answer.
I believe that the overriding principle should be:
If it's in a check list, the POH or otherwise mandated, then do it that way.  Not doing so could have legal, operational or insurance implications.
If it's not, then do whatever works for you.
If you check that you haven't taxied to the wrong end of the runway (it's happened before) by checking that your heading bug is pointing at the runway you are about to enter or some other check which is in your setup, then keep doing it.
By all means, look for practical, actionable suggestions that make sense to you instantly then consider incorporating them but pilots changing habits, whether by choice or if required to do so, is a continued source of accidents.
For example, I do like @rbp comment to you about COM1 and COM2 being on the belly or the roof.  That's a good one I hadn't heard before.
It's fine to ask for opinions, although it might get the question closed, but how can you trust random strangers on the interweb thing?  Being consistent, logical and above all, true to the way you fly is I believe the most important thing by far.


text:
How does a pilot switch from IFR to VFR mid-flight?
I had a pilot tell me that a rude ATC controller was making him fly way off route and through clouds and turbulence. So he switched to VFR and climbed out of the mess and towards the direction he wanted to go. Without getting into who was right or wrong in this particular situation, how does one cancel IFR mid-flight?

I wouldn't consider this a duplicate since it sounds like the pilot just canceled IFR and went on their merry way. VFR-on-top is still an IFR clearance and you must remain on the cleared route unless deviation is authorized.

You simply tell ATC your request:

A: DEXPL, request cancel IFR.
  R: DEXPL, roger, report VMC.
  A: DEXPL, we are VMC.
  R: DEXPL, IFR cancelled at 20. Squawk VFR, approved to leave frequency.

Yes, it really is this simple. The operative words are "Cancel IFR". You can even ask to maintain the current squawk code for VFR flight following (in the US, at least).

what is the "cancelled at 20" part?  Is that a Zulu time? An Altitude?

@abelenky Minutes after the full hour.

What if you are not yet vmc? Will atc vector you to a vmc area before canceling?

@TomMcW How would ATC know where VMC is? :) Pilot needs to indicate where he will be VMC and he will be vectored there.

So you request, for example, an altitude change that will get you out of the clouds then ask to cancel? I presume you let them know that you are wanting to get out of imc so they know why you're asking?

The US also have the concept of VFR-on-top, which is still IFR. I am not familiar with that though... so yes, I would essentially tell ATC I want a climb or descent to get into VMC with the intention to cancel IFR.

Just a couple points to make:  1.)  Cancelling IFR is not a request, you are telling them you no longer required their services.  2.)  In most cases you are doing the controller a favor by reducing their workload.

@MichaelHall In ICAO/EASA ops it's a request, because ATC can deny it temporarily. I believe in FAA-land, you can simply cancel without approval.


text:
How do you know what equipment code to put on a flight plan?
Every time I have flown and filed flight plans the CFI or the person I have rented the plane from has told me what equipment code to put on the flight plan. I am curious how you would figure out on your own. Is it in the POH?

FAA or ICAO flight plans?  (The formats are different.)

I don't like link-only answers, but Wikipedia has a great answer to this question https://en.wikipedia.org/wiki/Equipment_codes

Basically you know what equipment is installed on the aircraft (and in working order), and that's what you enter on the form.
For FAA flight plans, there's a list in the AIM (It's table 5-1-3).
Generally for domestic flight plans you file the "best" equipment you have onboard in working order.
FAA "Domestic" flight plans are eventually going away though, and we'll be expected to use the ICAO flight plan format (including its equipment codes).
ICAO equipment codes are a little more complicated because the "Equipment" box lets you list a whole lot more stuff (and the more you enter the more ATC knows in the event of an emergency): Basically you list all the equipment you have in working order under the equipment box on the ICAO flight plan form.
Lists of ICAO equipment codes is available (the one on Wikipedia is pretty complete), and there are handy wizards floating around that let you check boxes and get the string you need to enter on the flight plan.

Look at two hypothetical aircraft, both identical Cessna 172s with different equipment to see how it works:

Aircraft #1 has a VHF Nav/Com (VOR only, no ILS), DME, GPS, and Mode C transponder.
This aircraft would file /G on a domestic flight plan, and DGOV/C on an ICAO flight plan (the ICAO flight plan may also include R and an appropriate PBN code for the GPS capability).
Aircraft #2 has a VHF Nav/Com with ILS capability, and a Mode C transponder.
This aircraft would file /U on a domestic flight plan, and SV/C on an ICAO flight plan.

Note that the ICAO flight plan gives ATC more information to work with:
If Aircraft #1 calls up and says their GPS died ATC knows they can assign them clearances that use VORs and DME for navigation, but that the aircraft cannot accept an ILS approach at their destination.
Conversely if working off a domestic flight plan ATC will have to ask the pilot what their navigation capabilities are (or they may assume "standard" equipment including an glideslope receiver and ILS capability and offer the pilot an ILS approach only to be told "Unable ILS" by the pilot).

Could the pilot of Aircraft #1 fly a LOC approach?

@UnrecognizedFallingObject No, you must have an ILS receiver to fly a LOC approach (not even WAAS allows you to fly a LOC approach).

It isn't just in the even of an emergency:  They use the equipment codes to know what kind of arrivals and approaches they can assign to you (for instance, RNAV 1 SIDs and STARs, etc.)

Even worse, aircraft #1 simply can't fly ILS or LOC approach at all and the domestic flight plan gives no indication of it. So even without emergency ATC is likely to offer ILS approach just to get "unable ILS" back (of course, VHF Nav without ILS capability is probably quite rare).

@JanHudec I've never seen it, and the particular combo of equipment I gave would be very unlikely (DME without ILS? Witchcraft!). Something like a single Garmin GPS/Com unit and a transponder would give you /G by way of GV/C though -- a plane that couldn't even do VOR navigation if its GPS died - you'd be reduced to radar vectors to someplace VFR, or a surveillance radar approach!


text:
How does a constant pressure chart affect your preflight planning?
Would you choose a route or altitude based on the information in a constant pressure chart? How does a constant pressure chart help a pilot plan his or her flight?

As others wrote, I don't think in and of itself the constant pressure chart will help with a go or no-go decision by itself.  However, I do believe it would help to get the big picture of what's happening with the weather; fronts, etc.  Knowing the big weather picture is more important depending on what kind of flying you do.  The constant pressure chart can help with that.  Regarding choosing a flight level or altitude to fly in I would use winds aloft, airspace charts like a sectional, anticipation of ATC given altitudes in the area you plan to fly in, etc.  Like many others have said: with regards to weather the more you know the better off your preflight planning will be and the constant pressure chart adds to your knowledge of the weather.

A constant pressure chart by itself doesn't provide any useful data for flight planning.
As it shows a height of a given pressure level, you can make some assumptions about air mass temperature and pressure systems. You could also determine wind velocity and direction to some accuracy.
However most of the information available is usually shown in a pre-computed and pilot-friendly way in other charts, such as sw-charts and wind/pressure charts.

A constant pressure chart by itself doesn't provide any useful data for flight planning If that is the case, then why are they produced? Crews piloting aircraft in the flight levels may find them useful for flight planning since they are flying on a constant pressure surface such as those depicted in these constant pressure charts.

Maybe the main target group is some other than aviation or flight planning?

I do think the main target group would be the meteorologists that produce the charts, but that does not mean that they are not useful to pilots for flight planning. I have used them frequently myself, even for flights under the flight levels; for example, the 500 mb chart shows winds that primarily effect storm movement.

Thanks for clarifying. That also explains our differences of opinion. On the US version wind is drawn. On the European version, only the height of pressure level and temperature are drawn. This means that in Europe, it doesn't even directly state the wind. We have different charts for that.

I don't know what charts you are looking at, but they are available with wind depicted.

The chart you linked is produced by University of Wyoming, hence the US format. Ours would be the same, but without the wind drawn to it (standard).

Never the less, as an airline pilot, I've never seen or used one in flight planning.

@Sami the wind at the levels those charts are produced for are generally geostrophic, so the wind barbs are parallel to the height contours.  e.g. if all you have are the height contours then you can infer almost everything about the wind direction and make judgments about where it is fast and where it is slow.  As an additional utility you are going to burn slightly more fuel flying from low heights to high heights and save a bit of fuel going the other way.  You might not directly use this, but whatever software your dispatchers use might take it into account.


text:
What are the restrictions on performing intentional spins?
I know there is controversy over the safety and utility of performing spins for training, but what are the regulations limiting them for training (solo and dual) or 'just for fun'?

Normal upright 'just for fun' one turn spins are great, subject to the caveats in the answers.  If you are interested in moving beyond that, PLEASE contact your local IAC chapter to find expert dual instruction.  There are many types of spins and the recovery control inputs required will vary based on type and aircraft.  In the right aircraft at the right altitude with the right training they're a blast.  I love spins and firmly believe in spin training.  I also know of people who've died because they couldn't recover from a spin in time.

There are at least three FARs that apply (maybe more?). First, "aerobatics" as defined in 91.303 seems to include spinning:

For the purposes of this section, aerobatic flight means an
  intentional maneuver involving an abrupt change in an aircraft's
  attitude, an abnormal attitude, or abnormal acceleration, not
  necessary for normal flight.

That means the general restrictions in 91.303 would apply:

No person may operate an aircraft in aerobatic flight—
(a) Over any congested area of a city, town, or settlement;
(b) Over an open air assembly of persons;
(c) Within the lateral boundaries of the surface areas of Class B,
  Class C, Class D, or Class E airspace designated for an airport;
(d) Within 4 nautical miles of the center line of any Federal airway;
(e) Below an altitude of 1,500 feet above the surface; or
(f) When flight visibility is less than 3 statute miles.

Second, spinning an aircraft not approved for spinning in the POH would be a violation of 91.9:

§91.9   Civil aircraft flight manual, marking, and placard
  requirements.
(a) Except as provided in paragraph (d) of this section, no person may
  operate a civil aircraft without complying with the operating
  limitations specified in the approved Airplane or Rotorcraft Flight
  Manual, markings, and placards, or as otherwise prescribed by the
  certificating authority of the country of registry.

Finally, 91.13 would also prohibit spinning a non-certificated aircraft because it's a 'catch-all' regulation:

§91.13   Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation. No person
  may operate an aircraft in a careless or reckless manner so as to
  endanger the life or property of another.

But spinning itself is absolutely legal and is required for a flight instructor rating as described in 61.183.
EDIT: there's also a requirement in 91.307 that if non-crewmembers are on board then parachutes are required for maneuvers with 'extreme' bank or pitch, unless the flight is a test or training flight:

(c) Unless each occupant of the aircraft is wearing an approved
  parachute, no pilot of a civil aircraft carrying any person (other
  than a crewmember) may execute any intentional maneuver that exceeds—

A bank of 60 degrees relative to the horizon; or
A nose-up or nose-down attitude of 30 degrees relative to the
  horizon.

(d) Paragraph (c) of this section does not apply to—

Flight tests for pilot certification or rating; or
Spins and other flight maneuvers required by the regulations for
  any certificate or rating when given by—
(i) A certificated flight instructor; or
(ii) An airline transport pilot instructing in accordance with §61.67 of this chapter.

Great answer. Maybe you could add a bit about when a chute is/isn't required?

@kevin42 I've added a reference to 91.307, which I guess is what you're referring to?

Yes, and I think it's worth noting AC 61-67C paragraph 301, which says:"Section 91.307(d) states, in
pertinent part, that section 91.307(c) does not apply to flight tests for a pilot certificate or rating; or
spins and other flight maneuvers required by the regulations for any certificate or rating when given
by a certified flight instructor (CFI) or an airline transport pilot (ATP) instructing in accordance
with section 61.167."

The point I'm trying to make in the above reference is that the FAA considers flight maneuvers required by any certificate or rating when given by a CFI to fall under this exemption. So a PPL (student  or otherwise) being instructed  by a CFI would fall under this exemption even if they aren't currently working on a rating or certification.

The AC that kevin42 references has some very good information in it about spin training. It doesn't matter what rating you're working on. You aren't required to wear a parachute if you're with a CFI practicing spins. But DEFINITELY make sure that your aircraft is rated for spins. And fly with a CFI who knows the spin characteristics of that airplane. I'd spin a 152 all day. But I don't even like to stall a Piper Tomahawk. It's a decent trainer. But a BAD spinner.


text:
What process do I follow to land a civilian aircraft on a military base?
Let's say I have business on a US military base (e.g. JBLM), and I'd like to fly a privately owned aircraft there. What is the process I follow before the flight to get approval to land, and once I'm enroute to ensure everything goes smoothly?

Having never done it the best advice I can offer is "Contact the base WAY before you're airborne - like weeks out - to get permission." Since you've got business on the base maybe ask the folks you're dealing with to put you in touch with the officer in charge of the field - having the request brought to them internally would probably help. If you don't get an answer & manage to find out more about the process on your own please let us know - I'm curious myself :-)

Sneak it in really low.  Stick between all the little hills on the approach and dodge between the houses, certainly not above 30 feet.  At the last minute, pop it up over the fence and plonk her down.  You'll be parked before anyone even notices.  I'm curious to know how it goes.  Let us know how it worked out ;)

@Simon It will probably help if you paint over all the markings on your aircraft and switch off your radios. :-)

@Simon well, it worked for Red Square :) https://en.wikipedia.org/wiki/Mathias_Rust

Landing at a US military base isn't all that hard (I've landed at Ft. Drum before), you just have to get prior permission (PPR) (submitted at least 30 days in advance and confirmed within 24 hours according to 32 CFR 855.8), and need to have a "good reason" (as determined by them).
32 CFR 855, Table 1 (which is quite long) includes the purposes that are normally allowed.
You will be required to submit the following forms to the base commander (See the A/FD):

DD Form 2400 - Civil Aircraft Certificate of Insurance
DD Form 2401 - Civil Aircraft Landing Permit
DD Form 2402 - Civil Aircraft Hold Harmless Agreement

32 CFR 855 contains the regulations pertaining to US Air Force airfields (and the rules are similar for each branch).
855.1 - Policy includes:

(1) Normally, landing permits will be issued only for civil aircraft
  operating in support of official Government business. Other types of
  use may be authorized if justified by exceptional circumstances.
  Access will be granted on an equitable basis.
...
(3) Any aircraft operator with an inflight emergency may land at any
  Air Force airfield without prior authorization. An inflight emergency
  is defined as a situation that makes continued flight hazardous.

855.5 - Responsibilities and authorities. includes:

(6) Will not authorize use of Air Force airfields:
(i) In competition with civil airports by providing services or
  facilities that are already available in the private sector.
Note: Use to conduct business with or for the US Government is not
  considered as competition with civil airports.
(ii) Solely for the convenience of passengers or aircraft operator.
(iii) Solely for transient aircraft servicing.
(iv) By civil aircraft that do not meet US Department of
  Transportation operating and airworthiness standards.
(v) That selectively promotes, benefits, or favors a specific
  commercial venture unless equitable consideration is available to all
  potential users in like circumstances.
(vi) For unsolicited proposals in procuring Government business or
  contracts.
(vii) Solely for customs-handling purposes.
(viii) When the air traffic control tower and base operations are
  closed or when a runway is restricted from use by all aircraft.

Most of the purposes in Table 1 fall under "you have business at the base", or when due to weather or airport closure the planned destination is unavailable. This includes contractor business at a colocated private facility. It seems to me (not a lawyer) that OP would be able to fly there, provided the paperwork has been filed and accepted.

Its funny how someone somewhere in the Government has already written a law or policy document for almost every scenario you can dream of. :)

@curious_cat Username checks out :D

A "Joint Base" does not refer to joint military and civilian, it refers to Joint as in co-use by multiple branches of the services.  If you show up unannounced as an emergency aircraft, they will not point guns at you or detain you, they will simply handle your situation, provide the help and resources you need to get the aircraft back in the air and send you in your way.  There are only a couple bases that have "security at the ready" and will meet you with armed individuals.  The military is not some war-crazed institution waiting to shoot people, the bases are staffed with civilian controllers as well as a military and they are there to help when and where they can in aviation.  My experience flying both military and civilian aircraft for over 30 years has only produced professional accolades for the folks on the bases around the world.  If you have official business, it should be easy to land there with prior permission, if not- don't go or ask. If you have an emergency, do not hesitate to use the installation, it is funded by your tax dollars and they will be happy to share.

I love this answer, but any chance you could include a reference, preferably military, that goes into greater detail?

@egid, Mr BBT said that he had experience flying military planes.  Is that not a sufficient "reference?"

That's great, but as a pilot it's nice to have regs to refer to. Especially when the FAA wants your cert, or something.

I'd never heard of JBLM but I guess you're referring to Joint Base Lewis-McChord which has the identifier KTCM? Airnav says it's joint civilian and military use, AOPA says it's private military, but the AF/D says it's joint, which should be the definitive answer.
If so, as a joint field then civilian flights should be OK but I would carefully read the entire AF/D entry as well as any other information it references and if you have any doubts or concerns at all then you should contact them in advance. Even if you don't, I would still contact them anyway and in this case the AF/D tells you to do exactly that:

tran acft parking extremely ltd. 24 hr prior coordination rqr

Landing at a private military field on the other hand would require special permission from the military which I assume is very unlikely to be granted unless you have good connections on base.
Update from an anonymous user:

The reason that AirNav says 'joint military/civillian use' is that at
  one time KGRF (the airfield on the Army side of JBLM, then a separate
  installation - Fort Lewis) had an 'Aero Club' that operated a flight
  school & rented Cessnas for use by the base population. They also
  allowed troops who owned personal aircraft to base them on field at
  the Aero Club.
That Aero Club facility closed due to insufficient use during the
  height of Iraq/AFG deployments, and with it civil use of the JBLM
  runways ended. The ramp space is now used by military aviation units
  (an Army Combat Aviation Brigade) that moved to JBLM after the Aero
  Club closed.

Back when I was a student, my instructor had a genuine emergency and had to land there unscheduled.  Despite being listed as joint civ/mil, they were a little hostile there.  I would not treat JBLM as a civilian airport. Its military-only.

@abelenky That's good advice, I wouldn't treat it that way either and the comment I quoted from the AF/D hopefully makes it clear that you can't just turn up unannounced.

Note that the regulations specifically allow emergency aircraft to land at military airports.   They might not like it much, but it is allowed!

Yeah they'll let you but even if it is an emergency I can almost guarantee you'll have security forces show up with guns at the ready if not pointed at you when you land

What would happen if you landed there without even contacting ATC?

The comments are all over the place on how to land a civilian aircraft onto a military airfield. Here's how you really do it:
1. Get signed copy of a DD 2400 from you insurance company.
2. Fill out DD Form 2401 and 2402.
3. Submit all forms to the military service HQ in Washington DC for the airfield you want to land on. Address is on the forms. (JBLM belongs to Army and Air Force. If you want to land on the McChord airfield, you have to have Air Force permission. Army airfield, Army permission.
4. Once permission is granted, you have to contact the airfield manager and submit documents required by the airfield manager.
Bottom line: You have to have an association with the military to land your aircraft onto a military field; i.e. active duty, retired, contracted. I've been landing at military airfields for over 20 years.


text:
Which ATC instructions should be repeated back by the pilot?
AIM 4-4-7 (b) says:

Pilots of airborne aircraft should read back those parts of ATC
  clearances and instructions containing altitude assignments, vectors,
  or runway assignments as a means of mutual verification.

As a student pilot soloing into class C airspace, on one flight ATC kept repeating everything back until I spoke it back to him. As I approached the airport he informed me of the bearing (12 o'clock) and distance to the airport until I acknowledged him (comms were pretty busy so I didn't initially repeat back his information).
Since then I've noticed that if I don't repeat back wake turbulence warnings verbatim they will repeat the warning until I do. With a traffic alert I repeat back immediately 'looking for traffic' because if I look first they'll keep repeating the warning.
Aside from AIM 4-4-7 is there any more specific guidance?

A note: if you're IFR and the controller wants to assign a visual approach you need to report the airport/runway in sight, and if the controller solicits that report they need to tell you the relative position of the airport. If you're VFR, pointing out the airport to you is over-controlling; you're expected to navigate on your own to the airport visually.

ATC is, broadly speaking, required to ensure that pilots hear, understand, and acknowledge information that is delivered.  The way they do that is via read-backs, and although the AIM mentions a few of the things that are required it's a good idea to read back anything that's important (If you're not sure, err on the side of "It's important"), with your aircraft callsign (No callsign? Doesn't count!).
What are some important things controllers usually expect you to read back?

Clearances (headings, vectors, altitudes, transponder codes, and radio frequencies).
Like the AIM says, mutual verification.
Runway assignments, hold short instructions, line-up-and-wait, and takeoff clearances.
Taxi routes Instructions, ESPECIALLY runway crossings & hold-short instructions.
Wake Turbulence advisories.
Traffic point-outs.
The magic words here, by the by, are "Negative Contact" and "Traffic In Sight".
I think if you say "Tally Ho!" you're required to buy everyone on the frequency a bottle of 30-year-old scotch.
Instructions to "Maintain visual separation with" some traffic
ATC is handing off collision avoidance responsibility to you as the pilot.
They need to hear "Will maintain visual separation with" the traffic in question.
They also need you to tell them if you lose visual contact.
Airport Point-Outs (Especially if there are several airports close to each other)
You can also pre-empt this by calling the controller: "Cessna 12345 has Podunk Municipal in sight", possibly with a bearing and approximate distance.
Landing Clearances
If you're in a busy pattern and they give you a sequence ("Number 3, cleared to land") they want to hear that part too.
That altimeter setting you get after a handoff.
(I blame Don Brown for getting me into this habit, but it IS a good one unless the frequency is crazy)

This list is by no means exhaustive, but it's most of the big stuff.

I'd like to see a definitive list. I regularly don't read back altimeter settings or wake turbulence advisories with no ill effects. However which runway you're cleared for, hold short instructions during LAHSO operations and VFR departure clearance you might receive at a class C airport when talking to clearance delivery - those are critical items that you are absolutely required to read back accurately. Not sure what you mean by an "airport point-out".

@seattle272SP The closest thing to a "definitive list" is in the AIM (Specifically, 4-3-18 when on the ground, and 4-4-7 when you're in the air). The list above includes those items plus ones the controllers where I am (metro NY) seem to like to hear. Re: airport point-outs, I thought this was self-explanatory from my example, but something like "Cessna 12345 do you have Podunk Municipal 3 O'Clock and 5 miles?"

OK - FYI the phrase "point out" has a specific meaning among controllers and it doesn't mean pointing out an airport to a pilot. I've not heard a fellow pilot or CFI use it.

@seattle272SP I'm aware of the specific meaning for controllers. There isn't really a phrase that fits here (It's not a "point-out" because it's not traffic cutting a corner of another controller's sector. It's not a "traffic advisory" because the airport is not traffic, and it's not an "airport advisory" because it's not related to field or airspace conditions) - if you can think of a better way to phrase it I'd welcome an edit as I agree the phrasing I used could be confusing :)

I've never been expected to readback a wake turbulence advisory, nor an altimeter setting. Not even once.

This little quote from the AIM is the source of a lot of confusion for new pilots.
In 4-2-3 (c), the AIM also says:

c. Subsequent Contacts and Responses to Callup from a Ground Facility.
You should acknowledge all callups or clearances unless the controller
  or FSS specialist advises otherwise.
  ...
  Acknowledge with your aircraft identification, either at the beginning
  or at the end of your transmission, and one of the words "Wilco,"
  "Roger," "Affirmative," "Negative," or other appropriate remarks;
  e.g., "PIPER TWO ONE FOUR LIMA, ROGER."

Let me make it simple:

You should read back those items that the AIM 4-4-7 specifies (and that you quoted in your question).  Basically any time that they give you a clearance or anything that contains a number.
You should acknowledge with at the bare minimum your aircraft call sign and preferably something that lets them know that you got their instructions/message and understand it, every time that ATC talks to you.

The one exception is after you have been handed off to the final controller on a PAR approach, you do not acknowledge their instructions.  They come too fast and you will have your hands full (and they specifically tell you this after your initial contact.)

As a short aside, you should know that there is case law which says that even when a pilot reads back a clearance incorrectly, the controller is not legally obligated to listen or correct the pilot.  They consider it the pilot responsibility to hear and understand all clearances.  For instance:

Controller: Cessna 1234, descend and maintain 3,000 feet
  Pilot: Cessna 1234, Roger, descend and maintain 2,000 feet
  Controller: No response
  Pilot: Descends to 2,000 feet because that is what he understood, and
  may now be violated for it.

That being said, most controllers are very good and catch mistakes like this that you may make, but I have heard conversations in the cockpit along the lines of "it must be right because they didn't correct me when I read it back" and this is a situation ripe for problems/violations.  If there is ever a doubt, ask for clarification!

Please consider posting something about that case law as an answer on this question: Is it ATC's responsibility to ensure read backs are correct?.  While the current answer addresses the asker's specific situation, you could provide a more general answer to the title question.

@JeffreyBosboom I wish that I had more time, but am at work and will be busy for a while, but you may want to take a look at this webpage and provide an answer of your own!

Regardless of what the AIM says, the practical rule I've always been taught is "read back all instructions". In other words, if ATC is telling you to do something then you must read it back otherwise they have no way to know if you understood the instruction correctly and will do what they expect you to. This includes clearance, ground and airborne instructions.
ATC information on the other hand is not an instruction (e.g. traffic advisories) so you only need to acknowledge it. But you should also read back altimeter settings because they're essential for maintaining altitude and therefore separation correctly.
And ATC is often very good at giving student pilots extra attention so even if they wouldn't expect a readback in other circumstances, they may have made an extra effort in the case you mentioned to make sure there was no possible misunderstanding.

+1 for "read back all instructions". Your readback doesn't have to be verbatim (especially on a crowded frequency) - just enough to convey that you've heard and copied the information correctly.

Not really an answer per-se, but I usually find it much easier to learn what NOT to read-back:

Weather information (except QNH (altimeter settings)), like wind speed/direction, etc
Time/hour/estimates (except EAT (expected approach time) when cleared to a hold)
Chatter (hey, it happens! don't read it back)

I can't seem to think to any others, though there should be a couple more. Anything else that doesn't fall into this will get a readback from me.

The answers here are correct. Just adding my perspective as a controller.

Runway hold short instructions. This is a required readback item. Super-high priority. We need to hear three things in one single transmission: "Hold short," the runway number, and your callsign. All three. In one transmission. We need it.

Runway assignment. This isn't quite as strong as the hold-short readback, I think it's still required but I personally won't be on your case quite as much about it. In any case I think you're supposed to read it back.

Visual separation confirmation. In order to use pilot-applied visual separation between IFR aircraft, we need to: 1) tell you about traffic, 2) hear you say "traffic in sight," 3) tell you "maintain visual separation," 4) hear you say "wilco" or "will maintain visual separation," and 5) hear your callsign in that same transmission. You can combine a step by saying "traffic in sight, will maintain visual separation, [callsign]." Another 100% required readback situation. Note: If you, as a VFR pilot, call traffic in sight, we assume you will maneuver so as to avoid crashing into them because that's what the FARs say you have to do. See and avoid. I won't tell a VFR pilot to "maintain visual separation" unless it's for wake turbulence and even then I kind of feel like it's extraneous.

Everything else is not required on our end, but come on, it's good to make sure we're on the same page.

Numbers. Altimeter, altitude/flight level, speed, heading, frequency, squawk code, etc. Common sense, I want to make sure you heard what I think I said, especially when it's a number and there's no context telling you a specific number would be right or wrong. Exception: wind check. You can read back the wind if you want I guess, but I'm not expecting you to.

Instructions. Pattern entry/extension, 360s, S-turns, taxi route, hold-position, follow, pass behind, route amendment (shortcut or reroute), etc. You can be judicious about reading back the instruction vs saying "wilco" based on frequency congestion, complexity of the instruction, etc—but it's good to say something so we know you heard.

Information/establishing two-way comms. Situation: You take off VFR, get switched to the departure controller, check on. Departure controller says "Radar contact" with no other instruction. Situation: You're on flight following and get a frequency change. You check on, "Podunk Approach, N12345 level 4500." Controller says "N12345, Podunk Approach, Podunk Altimeter 29.92." In either situation, have you established two-way communication? IMO, no!, you haven't yet! Please respond with something, even just your callsign, so each person knows the other party can receive their transmissions!

Traffic. If we call traffic it's for a reason. Usually it's because we judge that you might get too close to that traffic. (Sometimes we have to call traffic even though we have minimum vertical separation so you don't freak out if TCAS freaks out.) It's not a problem if you don't have the traffic in sight—if we need to we'll issue control instructions to keep you apart—but you should at least respond with "looking" or "negative contact."

Vectors to final. Essentially this is a specific case of the "numbers" and "instructions" bullet points. If you're getting vectors to an instrument approach, you will at some point hear "PTAC"—Position relative to apch fix, turn (heading) to intercept final apch course, altitude to maintain until established, clearance to fly the approach. This may be in one transmission or may be broken up. You definitely don't have to read back the position, and you might choose not to read back the heading and altitude (though I recommend it), but you should at least confirm that you understand you're cleared for the approach.

Basically there are extremely few situations where I am happy hearing zero response from a pilot. I don't need a full readback except for the three situations at the top of the post, but I don't like giving an instruction and hearing zero acknowledgement.


text:
Can I count PIC time when regaining night currency with an instructor?
Let's say I want to get night current again, but I haven't flown at night recently so I hire an instructor to fly with me. If I don't count PIC time I don't see a problem, I would just log it as dual instruction. But if I log PIC time, is the instructor considered a passenger? If so I wouldn't be able to have the instructor with me since I am not night current.
Is there an exception for flying with an instructor?

You can log PIC time because you are "the sole manipulator of the controls of an aircraft for which the pilot is rated" (14 CFR 61.51).  That's all that is required in this case for the pilot to log PIC time.
So since a pilot must be night current in order to fly with passengers, (61.57(b)) the question becomes, "is a flight instructor considered a passenger if they are providing instruction"?
AOPA has a flight briefing about this specific scenario where they quote FAA legal interpretations as saying:

"We agree that, for purposes of section 61.57(b), an authorized
  instructor providing instruction in an aircraft is not considered a
  passenger with respect to the person receiving instruction, even where
  the person receiving the instruction is acting as [pilot in command].
  (The instructor must be current, qualified to instruct, and hold a
  category, class, and type rating in the aircraft, if a class and type
  rating is required.) The instructor is not a passenger because he is
  present specifically to train the person receiving instruction.
  Neither is the person receiving instruction a passenger with respect
  to the instructor. This training may take place, even though neither
  pilot has met the 61.57(b) requirements."

Note that they say in this case, since neither of them is a passenger, that technically neither the pilot or the flight instructor has to be night current.

Here's the FAA's legal definition of a pilot in command from 14 CFR 1.1. Note that this is a definition completely independent from the requirements to log PIC time:

Pilot in command means the person who:

(1) Has final authority and responsibility for the operation and safety of the flight;
(2) Has been designated as pilot in command before or during the flight; and
(3) Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight.

On a flight like this, you may act as PIC of the flight as long as you are rated for the aircraft, and you may therefore log PIC time. The CFI can log PIC time, as an instructor can log all time spent instructing (this would count - you're working on your night landings). 14 CFR 61.51(e) covers the logging of PIC time.
If, for some reason, the pilot receiving instruction does not feel competent to act as the PIC, they can designate the CFI as the PIC based on item (2) of the definition in 14 CFR 1.1. If this is the case, as they're still sole manipulator of the controls, PIC time may still be logged by the non-instructing pilot.


text:
What aircraft model is on this old photograph?
I would be grateful if anyone could identify this - Copyright Real Photographs Co. No. 750

Hello Ken, can you give us more information about the photograph? where did you find it? Where was is taken? Maybe the year?

Comments are not for extended discussion; this conversation has been moved to chat.

Hi, Unfortunately I have no other information. The card was in a group of disparate aircraft postcards.

It's a Carden-Baynes Bee... A British plane built in the 30s...
https://en.wikipedia.org/wiki/Carden-Baynes_Bee

This one was not easy, congrats!

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What kind of input is used by NASA's TASAR?
I've found the Aviation SE to be a really interesting read so far, I'm excited to be here! I'm fairly new, but I'm also old!
What are the inputs for TASAR to crunch flight path optimization? Is it taking a look at the aircraft performance model, wind and weather, and ADS-B IN? Maybe TCAS-II traffic info? Would the weather data come from the onboard WXRadar or ground data?
I've read a few data-points that the long range weather info pilots tend to use is from received data (maybe ground radar or sat based weather data? both?), but the data is delayed to the point of being less useful, would the weather data need to take inputs from both Weather RADAR and NEXRAD type inputs?

Welcome to aviation.stackexchange!

The answer is "All of the above." The left hand side of this slide from a NASA Powerpoint deck pretty much covers your question.

The full slide deck from the presentation can be seen here.

Thanks Juan! Slide deck is a term i usually hear from Consultants. You're not a consultant are you, Analyst Kyle?

Yes, I an a long time consultant and freelancer, and I use my real name here. I don't know who is Analyst Kyle.

Sorry, google it, it's a silly joke among MBA consultants

@Jeremy I did. Still no clue. No worries. :)


text:
What are these things on strings after the loss of cabin pressure?
I saw a picture on Twitter after the loss of cabin pressure. I've seen these images many times before, but in this picture, there are some things on strings that I cannot identify.

Maybe the oxygen-masks used to be mounted on this white plastic things and now removed? Not sure though.

This looks like some maintenance going on.

They are the holders for the oxygen masks, they are packed into the plastic retainers and stored in the overhead, when the masks drop, they fall out of the containers. Not all systems have these retention pieces that I can find, but some do.
The "black" tubes (actually clear, but look black in the picture) you see are the oxygen mask tubes and the mask itself is dangling from the end of the tube, you can see they have green/red labels on them that signify they are oxygen. The oxygen generator for that group of seats/masks is under the label in the top "HOT HOT", oxygen systems get very hot when generating oxygen (just ask ValuJet).

As a semi-related comment, I've seen some safety videos where they say "If an oxygen mask appears, pull down to start the flow of oxygen" or "if a string appears, pull down." There's a white string with a yellow tag that says "PULL."  Why do some planes include a "PULL" string? Why would only a string appear as opposed to the mask itself? Is it in case the mask gets stuck because they're packed so tightly?

I guess they can't guarantee that the mask will fall out of the retainer, so they cover it either way. Pulling down on the mask triggers the firing pin in the oxygen container to begin the chemical reaction to produce about 15 minutes of oxygen, I think both the string and the tube are connected to that firing pin but I'd have to verify. I don't think only a string would appear, it would be both the string and the mask.


text:
Has there ever been an commercial airplane with rear-facing seats?
Has there ever been a commercial airliner that the seats have been facing rearwards? It sounds like rear-facing seats would be significantly safer. In addition, the procedure for rear-facing bracing (https://en.wikipedia.org/wiki/Brace_position), seems significantly simpler and more obvious than traditional methods.

I flew with my wife and two children on a Southwest flight. Since one of my kids was an infant in a carseat the flight attendants brought us to the back of the plane where the second to last row was rear facing. It was very convenient. Since the whole family were facing each other it made it much easier to deal with the kids.

Related: Are there examples (current or historical) of commerical aircraft seating arrangments beyond the standard today?.

Some airlines do offer rear facing seats in business/first class. However, this is more to save space than for increasing safety. For example, British Airways offers a mix of forward and backward facing seats in its business class.

Source: Forbes.com
BAC Hawker Siddeley Trident offered rear-facing seats while it was in service. (Note the visible cockpit).

Source: airliners.net
Armed forces of a number of countries use rear facing seats, like the RAF and USN in their C-2 Greyhounds.

"C-2A interior DN-SD-03-16988" by Camera Operator: PH1(AW) Shawn P. Eklund, USN - US Defense Visual Information Center photo DN-SD-03-16988. Licensed under Public Domain via Commons.


text:
How does fuel get to the engine during acrobatics?
Given that during acrobatics, extreme G-forces may be impressed upon the fuel tank, wouldn't it make it somewhat difficult for fuel to get to the fuel pump while it's being pushed against a specific direction for the duration of the stunt? Is the solution just not to do the stunt long enough to starve the engine of fuel?

Highly related (if not duplicate): Are engines fed differently in reduced gravity aircraft?.

The basic problem is that no matter how the aircraft's fuel tanks are designed, if there is an air gap in the tank, then there is an attitude and/or a g-loading that puts that air gap over the inlet to the fuel line running to the engine.
There are a lot of solutions to this problem. The first is exactly as you say; don't sustain any maneuver that starves the fuel pump (and by extension the engine) for a longer period than you have fuel in the lines to feed the engine. You can actually do a lot without the fuel system seeing a single hiccup in supply; the fuel tanks are designed to feed while under positive G-load (otherwise you couldn't get any fuel to the engine just sitting on the tarmac), so hard turns, rolls, loops etc that keep a force on the aircraft and its contents acting downward towards the floor of the cockpit will keep the fuel flowing into the engine. Spins and high negative-G maneuvers tend to be the things that starve the engine; if the tanks are in the wings, a hard spin, snap roll or zero-g parabola will push the fuel out away from the inlets at the wing roots.
Most fuel systems except on the lightest aircraft have at least two fuel pumps per engine; one electric pump on the tank side to shove fuel into the line, and one crankshaft-powered pump that draws fuel out of the lines into the carb chamber or other fuel delivery system. The checklist often involves turning on the electric fuel pumps just before startup to prime the fuel lines, then turning them off once the engine is running smoothly, but you can keep the electric pump on if you plan on really twerking the aircraft in flight. The line between these two pumps actually holds a fair amount of fuel, plenty for a minute or more of sustained operation with the inlet at the tank totally starved, and coupled with a bleed valve on the engine side to release any air that's entered the line, the two pumps running together can usually keep an uninterrupted flow of fuel into the engine by having the electric pump shove fuel down the line as fast as it can whenever the inlet is under the liquid level.
For mild aerobatic maneuvers, a "flop tube" is put into the fuel tank. This is simply a flexible hose with a weight, that keeps the hose under the liquid level, no matter what forces are acting to move the mass of liquid around in the tank. This is a simple and very effective way to keep fuel flowing to the engine while the aircraft is under load in any direction, but because the flop tube requires a significant volume of fuel to sink underneath and draw from, flop tubes can increase the "unusable fuel" capacity of the aircraft (fuel that exists in the tank, but the fuel system can't draw out in some normal circumstance). However, there's a tradeoff; the heavier the weight on the end of the flop tube, the more reliably it will stay under the fuel level regardless of attitude, but the more force with which it will impact the sides of the tank in violent maneuvers (and padding the weight further increases unusable fuel).
For the real aerobatic nuts, though, the maneuvers are so violent and so long that even a flop tube, redundant fuel pumps and bleed valves might get starved as the fuel sloshes and churns and there isn't a real "liquid level" to draw from. Many of these aircraft go one step further; a bladder-style fuel container. Within the fuel tank is a flexible polymer vessel that actually holds the fuel (typically in either wingtip tanks or a fuselage tank; it's usually impractical to try this with in-wing tanks). This bladder keeps the liquid and gas in the tank shell separate as the tank empties, and may also keep the fuel under some static pressure. If there's no air to draw into the fuel lines, then no matter how the aircraft is oriented or how many Gs it's pulling in any direction, the fuel lines can't be starved.
Of course, the fuel lines are only one consideration. Most "normal"-rated aircraft have float-type carburetors, which hold a reservoir of fuel with another air gap, and the fuel level in the reservoir is controlled by a float that opens the inlet from the fuel pump (this system also deals with small hiccups in the fuel flow from the tanks; the air just forms part of the air gap and the float keeps the inlet open until fuel flows in to raise the level). This type of carb will starve the engine during any maneuvers involving less than 1g of force acting towards the "floor" of the float chamber, as the float will keep the inlet closed and the reservoir will starve the fuel feed tube that allows fuel to dribble into the throttle body at the throat. For aerobatics, either a diaphragm-chamber carb (which has a flexible wall on one side of the reservoir chamber that is connected to the fuel inlet) or a fuel injection system must be used to avoid dependence on gravity to get fuel into the engine. The downside of these systems are increased complexity, and in the case of the diaphragm-chamber carb, intolerance of air this far along the fuel system (requiring an air bleed to purge any bubbles in the line before the fuel enters the reservoir).

What about military aircraft? They must go through a lot of g's & weird attitudes?

Military aircraft use a combination of these techniques; internal fuel tanks and CFTs are often bladder-style, while droptanks usually have a flop tube. Wing tanks typically can't use any of these, so redundant fuel lines with pressure-actuated valves can be used. An air bleed is common, with the air fed into the compressor stage instead of the combustion chamber, and last but not least, fighters are designed primarily for high positive Gs; human pilots usually can't tolerate more than 2 negative Gs before "redding out", so a plane that can feed fuel at -4G isn't really much of a concern.

It might become important for the military drones?  They don't have to be limited by pesky human limits. Or do drones not enter any very extreme G manouveres in the duties they are typically currently assigned to like Recon etc.  Ha, maybe at some point we will have drone dogfights?

Eventually, but for now the lag inherent in the remote control systems of the Predator prohibit much more than lazy patrol circles. The Predator system in use in Afghanistan/Iraq requires someone in line-of-sight to take over during TO/L, because the guys doing most of the piloting in Nevada have a full 2 seconds of lag between making a control input and seeing the drone's reaction. That would be totally unacceptable in an air-to-air dogfight. Perhaps another question is, if an adversary nation deployed drones, would taking one out with an F-16 count as an A-A kill?

There are a few different types of acrobatic fuel systems but there are specialized fuel systems for acrobatic planes for this very mater. The FAA has a nice document covering it here.

For acrobatic category airplanes, excessive loss of fuel during
  acrobatic maneuvers, including short periods of inverted
  flight, must be prevented. It must be impossible for fuel to
  siphon from the vent when normal flight has been resumed
  after any acrobatic maneuver for which certification is
  requested.

This article cites at least one way of doing it.

To ensure the flow from fuel tank to fuel injector, aerobatic aircraft with the fuel tank in the fuselage have a “flop tube,” a flexible hose with a weight in the free end, plugged into the fuel tank

And here is another question on how fighter jets do it.


text:
What component of an aircraft is most likely to fail?
Given how rare airplane component failures have become today, I'm curious, are there still any components which are commonplace on aircraft, but still see a high failure rate? If so, why are these components used?
If not, are there any specific regulations to prevent this kind of thing?

The pilot. They're still widely used in aircraft and fail - or at least are part of the failure chain - in many accidents. Despite numerous regulations that apply to them, there is no viable alternative yet.

the tires ?????

The nut that holds the yoke.

It's a difficult question to answer, unless you limit the scope. What is the problem if a display fails? There are backups. But if you ask only for failures that led to incidents or accidents, then the question may be easier to answer (only an assumption).

There are many components that are non-critical and/or have a backup. These failures would only be logged in individual plane MX records

the flight catering

@Airsick many sources (I think the same as yours) seems to show that if one fail, the other won't until the aircraft is landed. Note that it is better than engines which may all fail together in case of fuel contamination.

Aside from the obligatory "The Pilot" answer, there are some components on an aircraft that will certainly fail at a higher rate than other components.
From the Piston GA side of the equation I can name a few (some of which are also applicable to turbine aircraft).

Incandescent Light Bulbs
A lightbulb is a supremely unreliable device: A delicate bit of wire is suspended in a thin glass envelope and heated until it glows - then subjected to vibration (from the engines, turbulence, etc.) in flight. We use them all over the airplane -- Position lights, landing lights, cockpit instrument lighting, etc. If you think about how often incandescent light bulbs burn out in your house it's probably not surprising that they fail quite often on aircraft. One such failure lead to a famous crash.

We still use incandescent lightbulbs because they're cheap: A $0.25 light bulb can be replaced multiple times before its cost even approaches the capital investment in a better solution.
  Modern aircraft are incorporating an increasing number of LEDs to replace incandescent lightbulbs - these solid-state devices have a lower failure rate (and other benefits).

Batteries
Much like your car aircraft rely on batteries for some functions (like starting the engines or the APU). Batteries have a finite service life and will eventually fail to hold a charge and need to be replaced.
Sometimes battery failures can be rather dramatic.

We still use batteries because hand-propping aircraft can be dangerous, and getting the APU turbine up to speed without a battery would be nearly impossible. Also if the engine-driven generators fail the battery is a useful source of electricity to help you get to a safe landing site.

Spark Plugs
Piston engines are spark-ignition, and spark plugs have a variety of failure modes (they can become fouled with lead or carbon deposits, the internal resistor can fail, or the electrodes can simply wear out).
These failures are not uncommon: Statistically if you fly piston aircraft long enough you'll probably encounter at least one of them.

We use spark plugs for obvious reasons: Unless the fuel is ignited it doesn't generate any power. Without power the propeller doesn't turn (at least not very fast), so there's no thrust. No thrust means no flying.

Tires
Tires are another aircraft component with multiple failure modes. Interesting ones include leaks (air leaving the tire at a rate fast enough to be a problem), "catastrophic" failures where the tire explodes or disintegrates while rolling, and "self-protective" failures (where the tire reaches a temperature that melts the fusible plug and causes it to deflate to prevent it from exploding).

Tires are also used for an obvious reason: Aircraft that constantly belly-land require expensive maintenance (to say nothing of the damage they do to the airport), and the alternatives - skis, pontoons, or flying boats - are limited in the areas from which they can operate.

Air Filters
On piston engines there is normally an intake air filter which is designed to keep dust and grit out of the engine. These filters can fail by becoming clogged (which I suppose isn't really a failure: The filter is doing its job), and certain paper filters can fail by disintegrating and being ingested into the engine (the FAA has issued airworthiness directives on this subject).

We still use air filters - even the paper kinds that can disintegrate - because ingesting dirt into a piston engine greatly accelerates wear. The required maintenance on the air filter costs less than increased overhaul frequency.


text:
If a pilot waves back, does it violate the sterile cockpit rule?
There was a video posted to Reddit of pilots waving back from their commercial jetliners. What followed was a discussion of whether or not this was a violation of the sterile cockpit rule. Given that waving back is non-essential communication, is this a violation of the FAA sterile cockpi rule?

The vast majority of the cockpits in the video have nothing to do with FAA rules.

One can aswell flag every pilot waving at spotters... (lots of pictures on Airliners.net) Sometimes, I'm wondering whether we may end in a world where noone is allowed to move a finger because of safety concerns... I'm not saying this because of OP, but still...

From rgl.faa.gov

Sec. 121.542
Flight crewmember duties.
(a) [I omitted this, it's about noncritical (company) procedures]
(b)
  No flight crewmember may engage in, nor may any pilot in command
  permit, any activity during a critical phase of flight which could
  distract any flight crewmember from the performance of his or her
  duties or which could interfere in any way with the proper conduct of
  those duties [...] such as [...] engaging in
  nonessential conversations within the cockpit [...]
(c) For the purposes
  of this section, critical phases of flight includes all ground
  operations involving taxi, takeoff and landing, and all other flight
  operations conducted below 10,000 feet, except cruise flight.

One could argue that waving could distract the pilot taxiing, so according to the letter of the law, yes, you would violate the rule.
However, I think in the spirit of the rule it's fine, since it just means that the pilot not taxiing is paying attention to the surroundings as well. Reading between the lines, it basically says

(a) During critical phases of flight, all crew should focus on flying, not selling cooked cardboard
(b) Also, don't read the paper with a croissant while asking help with a crossword during said phases.
(c) Critical phases of flight are when you're likely to read the bumper sticker on another jet.

I don't think a quick wave is quite as severe a violation as e.g. reading the paper (or, as the FAA calls it, reading publications not related to the proper conduct of the flight) during take-off. Compare it with a bus driver waving to a fellow driver or one reading the paper while driving. But then, if you do park your plane in a ditch while trying to wave to your mom, don't be surprised to be held fully liable.

Violation of cockpit sterile rule : Me as a passenger in a 767 cockpit on final at RUN (TNR-RUN-SIN), in 1998, inside thunderstorm clouds and the captain smiling to me while asking "it's shaking hard, isn't it ?", and me answering "yeah, that's great ! I'm loving it !". Not a violation : Me as passenger in a 767 cockpit (TNR-MBA-CDG) around 03:00AM somewhere above Lybia at 37000ft, and me and the captain discussing astonomy, particularly about a very bright star (Venus) to kill the time.


text:
What is this device they bring on board from the jet bridge when we park?
Every time I deplane a Virgin America A320, I notice that they grab something from the jet bridge, and stuff it between the jump seats. I haven't seen any other commercial airlines with things like this.

It may be part of this

Is the black spiral cable part of the device? If it is, do you know where it is plugged?

@mins, it's plugged into a panel with a whole bunch of other stuff plugged into it on the jetway. Not super useful.

I'm wondering why this has the appearance of a sensor, rather than a switch or keyboard. From what I understand the jet bridge has no lock to prevent it from being retracted (accidents happened), and the auto leveler system, adjusting the bridge level while the aircraft weight changes, doesn't need more than the sensor wheel at the door.

Looks like someone forgot his umbrella...

@mins Loading bridges have key locks on them to prevent unauthorized operation. Agents are supposed to lock them when left unattended. And you're right, the bridge auto-leveler simply uses a sensor wheel at the door.

It is a temperature probe for the preconditioned air (PC air) unit.
Bleed air is required in order to operate the air conditioning packs on an aircraft*. Thus, either an engine or the auxiliary power unit (APU) must remain running, burning jet fuel.  PC air pumps heated or cooled air into the aircraft and allows the pilot to shut down the engines and APU to conserve fuel.
This is what the system looks like from the outside:

A probe (located in the passenger loading bridge) is inserted into the cabin to regulate the air temperature while PC air is hooked up and running.
Upon parking, ground crews will typically hook up both ground electrical power and PC air, especially if the aircraft will be parked for any length of time. Since the air hose takes some time to unroll and roll, PC air may not be used if the flight is a "quick turn" and the APU will be left running.
* Except for the Boeing 787, which has a no-bleed system.

Of course! An image of the cabin probe on the bridge (source).


text:
B-52s that are not in service demolished?
Have all the B-52s that are no longer in service already been "guillotined," i.e. chopped in two to make them no longer flyable?

No, some B-52H's in long term storage at the Aerospace Maintenance and Regeneration Group are in Type 1000 storage, which means,

Aircraft stored in near-flyaway condition. Can be stored without re-preservation for a period of 4 years. Aircraft stored under this category may be downgraded to Type 2000.

Note: This screengrab is from Google Maps and I'm not sure when it was taken.
The USAF is under the process of reclaiming a B-52H from the Boneyard as a replacement.

Source: foxtrotalpha.jalopnik.com
However, all the B-52G models have been destroyed in compliance with the New START treaty.

Not necessarily, according to this picture of the Boneyard there are still some intact full airframes (I believe those are B-52's)

(source)
For what its worth chopping an airframe in half only makes it no longer flyable in its current state. While it may sound crazy that is actually not an impossible thing to repair as long is its done properly. You can see some of the planes chopped up in the photo but I would assume that was done to either transport them to the boneyard (they were un-flyable) or they are going to be shipped out to fix another plane.

The photo is at least a few years old but they're probably not all gone yet.

Fair enough, but id say it provides some solid evidence they are at least not chopped up directly upon retirement.

It not only makes it unflyable in its current state, it makes it obviously unflyable in a way that even satellite photos can verify. Since the B-52s are implicated by arms control treaties, this is useful.


text:
What are the FAA currency requirements for a foreign based certificate?
I hold a FAA private certificate that is issued based on 61.75. I have single engine land and instrument ratings on the foreign license (EASA). My FAA certificate also has these ratings listed.
My question now is: What are the currency requirements to execute the privileges of the FAA certificate to fly in the US?
61.75 (e) states:

(3) Is subject to the limitations and restrictions on the person's U.S. certificate and foreign pilot license when exercising the privileges of that U.S. pilot certificate in an aircraft of U.S. registry operating within or outside the United States; and

This can be interpreted two ways:
a) The currency of a rating on the foreign license is a limitation or restriction and therefore the pilot needs to be current for both the foreign license (e.g. EASA 2 year check for SE land rating, and EASA 1 year check for instrument rating) in addition to the FAA required BFR and IPC/IR currency based on approaches etc.
b) The limitations and restrictions mean explicitly mentioned limitations (e.g. EASA PPL does not include night flying, so the US cert would have "VFR day only" listed as a restriction). The EASA license itself does not expire on its own and is valid as long as the pilot holds a valid medical. Therefore only the BFR and FAA instrument currency requirements apply to fly legally in the US.
So which interpretation is correct? Is there some other regulation which makes it more clear?
Practically "to be safe" I could just fulfill the EASA requirements every year/two years, but that is quite an effort (this can only be done by an EASA ATO which there are few in the US). It also adds additional costs.
I could also take the test(s) to get a FAA private and IR independently and everything would be FAA based only. That's an option but also requires time and effort.

If you have that situation, you should ask FAA's Office of Chief Counsel. There is no univocal position about that.
The first position is that your EASA license should not be expired (which is not a case because EASA licenses do not have expiration date) or revoked, and should not list explicit limitations (according to Krauzs 2012 and Grossman letters). In that case your 61.75 license is good to go even with expired ratings in the EASA one. The only limitation is a current medical (because the license is invalid without it).
The second position is that all your EASA ratings should be current too, so they can be considered as limitations of your EASA license.
The second position is just safer. Nobody will have questions to you: neither FAA inspector, nor an insurance company.
In any case, it is required to be current by the FAA rules (BFR, medical, approaches/holdings etc.). For example, here (especially see Dave's comment) one had a problem with foreign-based license without current US medical.
In your case I would take FAA tests and obtain a standalone license, and forget about the problem (it's what I actually did recently). If it is not an option, either keep your EASA license current (just in case) or request an official answer in paper from the FAA.
Related topics on pprune: here and here.

While your EASA license does not expire, your ratings (which form an integral part of the license for all intents and purposes) do expire.
Therefore I'd personally assume that I'd need to keep those ratings current in, which requires a checkride with an EASA certified flight instructor once a year plus a requirement for 12 hours logged time that year for an EASA PPL.
Time for that vacation back to the home country and an hour flying there maybe?
It's an extra cost of course, but it's peanuts compared to the other costs of flying, including the requirement to have an EASA medical for your EASA license to be valid, which medical is stricter than the FAA medical so probably means you won't need a separate FAA medical on top of it (but do inquire to make sure).


text:
How is unusable fuel taken into account in weight and balance calculations?
Unusable fuel is considered part of the empty weight for aircraft so when the aircraft is weighed the undrainable fuel is already included. Is there any time unusable fuel would be required to be listed either added or subtracted on a weight and balance form?

Since you've used the word "required", you may need a current specialist on the subject to get a truly valid answer.
That said, here's what I can tell you based on having written weight & balance software that was FAA approved for use at three different freight carriers in the period from 1988 through 2016 for B727, B747, DC-9, DC-8, and L-1011 aircraft.
That software made no provision for unusable fuel, as that was included in the basic operating weight. Also, the manual systems the software replaced had no provision for unusable fuel.
However, as I remember, the forms that came to me from the last weighing of the aircraft when adding an airplane to the program sometimes listed the unusable fuel, and sometimes the undrainable fuel as well, depending.
In other words, forms or software involved in the everyday calculation of weight & balance typically do not show unusable fuel. Forms involved in aircraft reweighing, whether due to maintenance or regulation, oft times do.

Edit - Seeing @Anilv's answer, I realized I may have misunderstood the question. I took "unusable fuel" to mean fuel that can not be physically delivered to the engines as opposed to fuel that can be delivered to the engines but should not be. Ballast fuel fits into that second definition. It physically can be delivered to the engines, but should not be. Using that second definition the answer to the question:

Is there any time unusable fuel would be required to be listed either added or subtracted on a weight and balance form?

is: Yes, there was an entry field for use for ballast fuel if such might be required to meet weight & balance requirements. On 747 freighters, for example, ballast fuel was on occasion used to move the zero fuel weight c.g. forward to be within limits. This was especially true for 747s that had been pax aircraft and had been converted to freighters. The addition of a cargo door well aft of the wing root produced a configuration susceptible to a c.g. that was aft of the aftmost zero fuel weight c.g. limit. The solution, if you couldn't arrange the cargo to take care of the problem, was to to put ballast fuel in the fuselage tank, which was the most forward tank.
While you were not supposed to burn that fuel, it was comforting to know that it could be used if you really needed it.

On the A310 freighter there is a 'Minimum Flight Weight' ie the take-off weight of the aircraft must be at or above this weight to depart. If the load is very light you need to add fuel (ballast) to bring the weight up to this minimum. On the loadsheet it is not included in the fuel figures but as correction to the Basic operating weight with the remarks 'Ballast fuel for MFW' or similar. This fuel is not usable as it would reduce the aircraft weight and bring it below the minimum required and therefore illegal.
Don't have the actual figures as its been 20 years since I worked with that particular type (and it was a b***h to get in trim too!).
Anilv

No I'm not talking about ballast fuel. The TCDS lists unusable fuel and a location, and that it must be considered as "empty weight". I know I've seen weight and balance reports that listed unusable fuel as being added to the computation. But why? The only reason I could come up with was the aircraft was hot off the assembly line and literally never been fueled so there was no unusable fuel in it when it was weighed so it had to be added on the form. Is that correct?

@AMT72 My guess is that you are correct, but I cannot say from a reference or first-hand experience that you are. Another comparable situation is when, for whatever reason but primarily for fuel system maintenance, they need to drain the fuel system. However, as I understand it, in some aircraft you really can't get easily all of it out, and thus you have "undrainable" fuel.

Please clarify again - unusable fuel due to pump or system failure is not what you're talking about, right? If so, is it possible that the unusable fuel you're talking about and the one that needed to be included in the mass & balance sheet refer to 2 different things?


text:
Where did the SOE agents sit in the 161 squadron Short Stirlings?
I asked this question on history.se, where it was recommended I repost here.

During World War II Special Operation Executive (SOE) agents were dropped into occupied Europe by No. 161 squadron of the RAF. This squadron used the Short Stirling bomber up until March 1945.
In the Short Stirling, the pilots were separated from the flight engineer and wireless operator. There is also this picture on Wikipedia, which appears to show the interior of a modified Short Stirling that could carry passengers?
My question would be: In a typical 161 squadron mission, where in the Short Stirling would the agent(s) be located?

IIRC, the agents dropped (with parachute) through a hole in the belly of the aircraft, just aft of the bomb-bays. So they would sit in that general area, so that they wouldn't have to move far with the 'chute attached. The position of the pilots is immaterial to this.


text:
Can a pilot drive an ultralight with folded wings on the shouder of a country road
Saw an ultralight with power driven wheels the other day.
This begs the question, can a pilot legally slowly drive an ultralight with folded wings stationary prop and powered wheels on the shoulder of a country road, say with a slow moving vehicle sign?

Probably.  But you won't know for sure until a cop stops you.

That would be a "motor vehicle". There are rules for operating a motor vehicle on the public roads, even the shoulder. All states have different rules, regarding potential max speed or horsepower.

Something like that happened in Australia. To the pub, naturally: https://www.bbc.com/news/world-australia-29876001

Love it @Ben, but the eejit left the engine running! What a complete moron!

Because if you are going to drive an unlicensed vehicle which is also a plane on the road, obviously it's better to do it drunk.

The FAA has no jurisdiction over the roadways.  It would depend on the locality, but it is reasonable to presume that in a rural area that permits non-street legal machines like farm tractors, ATVs, etc. would similarly allow an ultralight.

As an example, from the Virginia DMV: "Farm vehicle license plates issued by the Department of Motor Vehicles may be used on a vehicle used for farming purposes by anyone who owns, rents, or operates a farm of a size that reasonably requires the use of such a vehicle to transport agricultural products."
So farm vehicle is not an automatic "get out of jail free" card.